The present invention generally concerns a method for controlling a navigation device powered by a battery or a rechargeable accumulator, such as a satellite navigation device like a GPS, GLONASS or GALILEO (future European navigation system) receiver, and a navigation device implementing this method. The navigation device according to the present invention is intended in particular to be incorporated in a timepiece. In this regard, the present invention also concerns a timepiece including a navigation device of the aforementioned type.
The use of navigation devices, and in particular GPS receivers was, until recently, essentially reserved for a limited number of applications. Recently, such use has become commonplace and generalised, and more and more commercial applications use such devices. Within the framework of this generalisation, one now sees navigation devices integrated in portable objects of small volume powered by a battery or a rechargeable accumulator. Thus, portable objects integrating a navigation function, such as timepieces in the form of wristwatches, have been on the market for a short while.
One fundamental problem of such battery powered portable objects resides in their greatly reduced working autonomy. A navigation device typically constitutes a high power consuming module which, if it is permanently activated, quickly exhausts the capacity of the battery or the accumulator powering the portable object.
Various solutions have been envisaged with a view to saving energy in such devices. One of these solutions consists in particular in only activating the navigation device periodically for a reduced period of time in order to perform the necessary position and time measuring operations. A particularly interesting solution adopting this technique is disclosed in Japanese Patent Application No. 10-206520 in the name of Canon Inc., filed on Jan. 16, 1997. This solution consists in periodically deactivating a navigation device, for a variable period of time depending on the velocity of the device. For this purpose, the navigation device includes calculating means arranged to determine the velocity of the receiver on the basis of position and time measurements, and control means for varying the deactivation time of the receiver between two successive position measuring operations.
One disadvantage of the device disclosed in the aforementioned Japanese document lies however in the fact that the power consumption of the device is either maximum when the device is activated, or minimum when the device is deactivated. One perverse effect of this technique lies in the face that the battery or the accumulator used to power the portable object in which the navigation is incorporated, is subjected to strong periodic variations in power consumption. Tests performed by the Applicant have proved that this periodic charge quickly and substantially lowered the life time of the accumulator or battery used, thus reducing the working autonomy of the portable object.
The Applicant has thus been able to observe that, in practice, the navigation device disclosed in the aforementioned Japanese document proved unable to be integrated in portable objects of small volume, such as timepieces, in which the accumulator or the battery used as the electric power source constitutes a critical element which, if subjected to the constraints described above, would not have sufficient working autonomy.
The object of the present invention is thus to overcome the drawbacks encountered with the navigation devices of the prior art when the latter are periodically activated and deactivated as is shown for example by the aforementioned Japanese document.
The object of the present invention is thus in particular to propose a method for controlling a navigation device and a navigation device implementing this method so that the power consumption thereof is adjusted in an optimum manner according to the necessary level of activity.
A further object of the present invention is to propose a navigation device which proves perfectly able to be integrated in a portable object, such as a timepiece, powered by a battery or a rechargeable accumulator.
The present invention thus first concerns a method for controlling a navigation device the features of which are listed in independent claim 1.
The present invention also concerns a navigation device whose features are listed in independent claim 6.
The present invention further concerns a timepiece incorporating a navigation device of the aforementioned type.
Advantageous embodiments of the present invention form the subject of the dependent claims.
One advantage of the present invention lies in the fact that, unlike the navigation devices of the prior art, the power consumption of the navigation device is gradually adjusted as a function of the necessary level of activity. Indeed, the navigation device according to the present invention is no longer periodically activated or deactivated as is typically the case of the known navigation devices, but its operation or more precisely the operating frequency of the processing unit of the navigation device is adjusted and adapted as a function of the conditions of use. This results in considerably less significant constraints for the battery or rechargeable accumulator used to power the device.
The navigation device according to the present invention may thus advantageously be incorporated in a portable object of small volume and small capacity, such as a timepiece for example.